The invention relates to a fork light barrier, and in particular to a position determining device and/or method employing such a fork light barrier.
In order to detect the position of parts moving relative to one another, in conventional devices, fork light barriers are used with a light-emitting diode and two light sensors. Attached to one part at regular separations are so-called vanes and windows which move, according to the relative movement of the parts, between the light-emitting diode and the light sensors. If a so-called vane is positioned in front of a light sensor, the light stream from the light-emitting diode to the light sensor is interrupted. If a window is positioned between the light-emitting diode and the light sensor, the light stream is free to strike the light sensor. The arrangement of the light barrier or the size of the vanes and windows is selected such that, according to the electrical light barrier signals, both the distance covered and the movement direction can be determined. A disadvantage of the known devices for determining position as described above is that said devices can only detect position incrementally. In order to recognize a reference position, such as a start position or a zero location, a further sensor is required. This sensor is typically provided by means of a further fork light barrier which is interrupted in the whole region of travel of the moving body at one position by a single vane. The use of a second fork light barrier or of a second sensor and a further light sensor and a second, separate vane represents an undesirable additional outlay for the arrangement.
DE 102 45 170 A1 discloses a device and a method for positioning an optical component. Two detectors are provided herein which simultaneously detect different encoding means if the recording device is situated in a particular detent position. In a region between two adjacent detent devices, only one of the two detectors detects an encoding means. In this construction, it is not possible to easily determine the rotation direction from the light signals.
U.S. Pat. No. 6,586,719 B1 discloses a light barrier for determining the movement of two objects relative to one another. The TR pairs (transmitter-receiver pairs) are arranged alternately on opposing sides of the two moving parts. The moving parts have particular geometrical transmission or reflection properties. However, the structure of said geometrical surfaces and the evaluation thereof are too complex.
U.S. Pat. No. 5,648,645 A discloses an elevator speed detector wherein vanes and windows are arranged on a measuring strip in the elevator shaft. The measuring strip has two regions on which a plurality of vanes and windows having increasing size and spacing are arranged, in alternating manner. Furthermore, test marks are provided to preclude errors. The arrangement disclosed herein therefore also requires a plurality of optical interrupter paths (vanes and windows). Movement direction recognition is also not provided.
EP 2101197 A1 and EP 0 617298 B1 disclose simple fork light barriers which have only one transmission path.
EP 0 377097 B1 discloses an absolute position sensor for determining the position of a steering wheel, having a plurality of sensors which are arranged individually around an encoding disk.
The aforementioned known arrangements and methods employ various different approaches but do not enable any simple determination of the reference position, the incremental movement as well as the movement direction.